


Role Reversal

by TheProtobabe



Category: Undertale (Video Game)
Genre: Dom!Sans, Dominance, Ecto-Penis (Undertale), Established Relationship, F/M, Fluff, Fluff and Smut, Light Bondage, Oral Sex, POV Third Person, Penetrative Sex, Plot What Plot/Porn Without Plot, Reader has a vagina, Shameless Smut, dom!reader, ecto dick, reader is female, sub!Reader, sub!sans
Language: English
Status: Completed
Published: 2016-07-07
Updated: 2016-07-07
Packaged: 2018-07-22 01:49:27
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,251
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7413826
Author URL: https://archiveofourown.org/users/TheProtobabe/pseuds/TheProtobabe
Summary: <blockquote class="userstuff">
              <p>Third-person Reader x Sans. Reader has female pronouns and a vagina. </p><p>Sans is usually the one taking charge when it comes to their sex lives, but today, on their third anniversary, she wants to try swapping roles…</p>
            </blockquote>





	Role Reversal

**Author's Note:**

> Okay I haven't written smut in forever, so please bear with me. I hope you enjoy!

She was feeling mischievous today. She read the text her boyfriend sent in reply to a naughty set of photos she’d given him, teeth catching her bottom lip as it curled into a smirk.

**Sans <3: holy shit babe**

**Sans <3: i’m at work and now hiding a raging boner under my desk**

**Sans <3: whats gotten into u **

She chuckled to herself and settled her elbows on the bed, feet kicking idly behind her as she texted back.

**Me: More like what’s gonna get into me :P**

**Me: I’m just getting you ready**

**Sans <3: ready? for what?**

**Me: You’ll see. It’s a surprise ;D**

**Sans <3: jeez whatever it is i’m game. happy anniversary, btw**

**Me: Happy anniversary! Love you, I gotta go get ready.**

**Sans <3: wow now i’m rly curious. love u too**

Rolling off the side of the bed, she checked the time. She had an hour before he started his drive home, which gave her some time to freshen up and prepare. Tonight, she wanted to do something a little special. It was their 3-year anniversary, so she knew he probably had something planned for the weekend. It was usually how they celebrated; they were both more available on weekends, so any celebrations they had were put off until then. That meant that tonight was all hers, and she dearly hoped he enjoyed himself.

Sans always thought she was beautiful, no matter what, but she knew he liked it when she put in extra effort just for him. It was the gesture, really, though she was fairly certain that freshly-lotioned, soft skin, silky and done-up hair, a fresh coat of red lipstick, and sexy lingerie didn’t hurt in the slightest. Besides, it all made her feel desirable, and tonight she’d need the confidence boost.

She had barely finished setting up the chair and the items along with it when the sound of crunching gravel alerted her to his presence. She assumed a sexy position on the edge of their couch, heart hammering nervously.

 _You can do this. He’ll love it, because he loves you,_ she had to remind herself, and smiled as he stepped through the door.

She was trying to go for a sultry, teasing look, but she felt it light into an excited and happy grin as she watched his face go slack and turn a deep blue. He’d frozen in the doorway, eye lights flicking across her body from head to toe.

“Oh wow…” he said, in a quiet, almost reverent tone. Her smile got broader.

“Welcome home, sweetheart,” she purred. She was still nervous, but his reaction spurred her on. “Come here.” She crooked a finger at him and he crossed the room quickly, his expression turning devilish.

“Mmm, I like this surprise,” he said, and lowered his mouth to her neck, nipping at it like he knew she liked. His hands swept her hair away from her face and began exploring her shoulders, her collarbone, her breasts... Her breath hitched but she firmly pushed him away, standing up and assuming a commanding look. He blinked in confusion.

“Tonight, I’m gonna call the shots,” she told him, sounding more confident than she felt. “Now, I’m gonna need _you…_ ” she steered him backwards and he went with no resistance, still a little taken aback at this turn of events. “...to sit _right here_ for me.”

The back of his knees hit the chair and he chuckled, finally gaining his bearings. He seemed amused as he answered. “All right, babe. Whatever you wanna do.”

She gave him an appreciative smile, cupping his face in a loving gesture. He leaned into it, eyes closing partway. “Okay. So I want to try something that I’ve seen before, but I don’t want to do anything you’re uncomfortable with.” She leaned down and picked up what looked like a roll of red duct tape. “This is bondage tape. It only sticks to itself and is supposed to be safe to play with,” she explained, smirking as his eye sockets widened. “What’s gonna happen is this: I’m gonna tie you to this chair…” she leaned into him, putting a knee between his legs and caressing his skull. His hands automatically went to her hips. “..And I’m gonna have my way with you. How’s that sound?”

His eyes were going a little hazy at this point, his face flushing with desire. “That… yes, yes I’m okay with that,” he answered, voice husky. She felt her heart flip in her chest and she gave him a big smile.

“All right, sweetheart. Now, if you don’t like something, just say--”

“‘Red’, yeah, I know.” The two of them had played around with rough sex before, prompting them to use a tried-and-true set of safe words in the bedroom. Green meant that everything was great and enjoyable, yellow meant to slow down or go easy, and red meant that everything needed to stop right away.

She knelt down behind him, taking his hands and wrapping some of the tape around them so he couldn’t bring them to his front. “How’s that, baby?”

“You uh, do realize I can just teleport outta this,” Sans told her, chuckling at the pout she gave him in return. He tugged at the bonds, testing them and wiggling his fingers. “Feels fine.”

“Good. Don’t be a spoilsport! Let _me_ take charge for once,” she scolded, poking his spine. He snickered, but quieted down and let her get psyched up for what was going to be something new and exciting for them both. She went to his front, enjoying the sight of her lover tied up and ready for her. In fact, seeing him there, looking up at her, helpless and wanting her… it was enough to make heat shoot through her abdomen. She lowered her eyelids and moved close, bending down and taking his face in both hands. Leaning her forehead against his, she felt his soul buzz and resonate through his bones. “I love you, Sans.”

She didn’t give him time enough to answer before she pressed her lips to his mouth, where he’d been waiting for her. His body was made of magic, though not always tangible; right now, she felt it mold to her lips and tease them, just like a human’s mouth. The differences made him unique and purely Sans; his magic ran hotter than a normal human’s, and there was a pleasant tingling feeling it left on her skin. She hummed when his tongue slipped in, tasting, ravishing, dominating.

 _Not tonight._ With an assertiveness that surprised him, she tipped his face back, her thumb insistently pulling his jaw a little wider. She dove into his mouth, tongue sweeping across the canines that were a touch longer than a human’s. She forced his tongue back and laved at it with luxurious strokes as if petting a cat. His groan vibrated down her throat before she pulled back, a spiderweb-thin string of her saliva connecting them for a moment before it broke. With something akin to pride she noted the red lipstick stains across his teeth. Marking him.

 _“Mine,”_ she growled fiercely, her lip curling into something like a sneer when she saw how blown his pupils were. He looked positively dazed and already a mess, even though she’d barely begun. She gasped when he strained against his bonds to bite the flesh at her throat insistently. With insistent hands she pushed him back against the chair, teeth bared.

“What did I say about being in charge?” she growled, but he just smirked at her defiantly. “Not even sorry about it. Maybe my little pet needs punishing.” She gripped his chin between her fingers and tilted it up again, noting with satisfaction that his grin was faltering at her words.

“Wait, punish--” he began, but she cut him off with a finger at his teeth.

“Quiet. Pets don’t get to talk unless their mistress says they can.” She tapped her chin, grinning down at him through messy lipstick. The side of his skull had formed a few beads of sweat as she let the tension linger. Good. “I know just how to punish you.”

She backed away from him, just enough that his body wouldn’t be able to touch her at all. Giving him a wicked grin, she thumbed the edge of her panties. “Did you like those pictures I sent you, sweetheart? Answer me.”

He took a shuddering breath, anticipating her taking off the sheer fabric. When he was quiet for too long, she leaned forward, shoving her hands under his shirt. She searched blindly with her fingers until they found his tailbone and pressed, _hard_ . Sans’s body bowed against the chair and he gasped in both pain and extreme pleasure from her rough handling of a sensitive body part. “Yes! Yes I liked them! Fuck, _fuck_ , don’t--”

“Mmm, good boy.” She let up and his body relaxed, his expression far more wary of her. She dropped her character for a quick moment to check up on him, worried she may have gotten a bit too rough. “You doing okay, sweetheart?” she asked, her voice getting softer. The side of his mouth quirked up.

“Yeah. Green.”

She positively beamed at him before getting back into character, backing away and continuing his punishment. “What’d you like about them?” She thumbed at the edge of her bra strap, letting it fall off her shoulder but disallowing it to get any further. His eyes watched the movement hungrily.

“I… the fact that you sent them at all while I was at work… god, that was so _hot_ ,” he admitted, watching her as she pressed her breasts together roughly. The skeleton monster let out a shuddering breath. “All that skin… and you playing with your nipples, bitin’ your lip. You know how much I like that.”

“Yeah? What else?” she purred, looking him in the eye as she let her hands trace up the outside of her thighs, over her hips, across her belly and stopping just before they went lower. He swallowed noisily, despite not needing that function.

“The way you were touchin’ yourself, rubbin’ your clit and starin’ right into the…” He faltered when her hand slipped beneath her panties. “R-right into the camera, holy shit,” he breathed as she leaned against the couch, dipping her fingers into herself. He couldn’t see it directly, but the movement beneath the fabric of her underwear told him enough. She bit her lip, forcing herself to maintain eye contact as she fondled herself. She could feel herself flushing, and as she spread herself with her fingers she felt how wet she was getting from this.

“You wanna touch me, don’t you,” she purred, to which he nodded dumbly. He was practically panting now. “Bad pets don’t get to touch their mistress. You don’t want to be a bad pet, do you?” she pouted, letting out a breathy moan when her fingers played against her clit. “Will you be good now?” she asked.

“Yes…”

A chuckle came from deep in her throat and she approached him again. “Good. As a reward, do you want me to take something off?”

“God, please…” he groaned. He was trembling slightly; she could hear the bones clicking together. Deciding to give him a little mercy, she unhooked her bra from behind and slipped it off, leaving her topless, and got close to him.

She touched her right breast, circling the nipple. “Lick it,” she demanded, bringing it close to his mouth. Immediately he complied, like a starved man. She let out a shuddering breath and lowered herself down onto his thighs, straddling the armless chair he was tied to. His tongue circled the perked nipple eagerly, flicking against it and using all his favorite little tricks to make her feel good. “Ahhh, Sans…” she breathed. “B-bite it.” He complied with a growl and she gasped, arching into his mouth and grinding against his pelvis. “Stop.”

He followed her directions as she pulled back, his face completely blue, eyes hazy. He was dragging in deep breaths, panting like an animal in heat. She caressed his chest and went to work at unbuttoning his shirt. She’d had enough practice to do it blind now.

“Shhh…” She was at his temple, her hand trailing feather-light over his exposed floater ribs. His needy panting quieted immediately, though his chest still heaved. She smirked against his skull, noticing the immediate obedience when she shushed him. It seemed he was very eager to comply, now that she had him unraveling beneath her ministrations. “Mmm, good boy.” Her hand slipped under his sternum to play against the flat, smooth underside of each rib where they connected at the center.

Sans tensed, holding his breath. She kept stroking gently, frowning when he didn’t unwind. He wasn’t asking her to slow down, but she wanted to make sure he was enjoying himself.

“Sans…” She pressed a tender kiss to his chest. “Sweetheart.” She moved her mouth to a different spot. “Relax,” she murmured against his bones, leaving a soft, wet trail with her mouth as she simultaneously teased every single rib with her fingers, getting higher and higher inside his chest cavity. Slowly, she watched his shoulders lower, until he slumped against the chair with a little sigh in surrender. She smiled up at him; his pupils nearly filled the sockets, sweat beading at his skull, bones rattling. He was coming undone and nothing could be more beautiful to her. She licked her lips eagerly. “Now, I want to _hear_ you. Say my name, baby.”  

His teeth parted, showing the dull canines on either side. There was a soft glow coming from within as he breathed her name. “...p-please, I…” He hissed as she gripped his ribs roughly from the inside, hooking her fingers between the slats and pulling him forward by them with a growl.

“Did I tell you to say anything else? Answer me,” she demanded, eyes flashing. He seemed taken aback, but entranced, shaking his head as if he couldn’t even think of disobeying her at this point. The feeling was such a rush--usually he was the dominant one, bossing her around, expecting unquestioning obedience. She could see now why he loved it so much. “That’s right. Now.” Her eyelids lowered, a snarl still playing along her lips. “Keep saying my name.” She reached all the way up through his ribcage and to his neck with her right hand, circling the cervical vertebrae as if she was throttling him. The other hand toyed at his pelvis.

Having no internal organs or flesh meant that the gesture did nothing to restrict his breathing or cut off his words in any way, but the very thought of her holding that sort of power over him made something inside of Sans snap. Suddenly he was a writhing, begging mess, his face the darkest blue it had ever been in his life. His dick strained against the fabric of his slacks until it was painful, his legs shuffling restlessly just to move and get some sort of friction going. And all the while he was panting and whining, his lover’s name coming out in broken cries as she teased his body.

Deciding she’d had enough of tormenting him, she knelt down at his feet and looked up at his face. She didn’t break eye contact as she undid his belt and shimmied his pants down over his thighs. His erection sprang free; he hissed her name again quietly at the feeling. She licked her lips, glancing down at it hungrily before shifting closer. She placed a kiss on his thigh bone, just behind his knee, and traced her fingers along the wing of his hip.

“Tell me what you want, Sans.” Another kiss, a little higher. Above her, he took a shaky breath and stammered. She smirked against his leg. “Hm? What was that? I can’t give you anything unless I can understand you, baby.”

“God, please, just…” He groaned brokenly when her breath ghosted across his cock, her mouth not going any further as she waited expectantly. “P-put your mouth on it, _fuck_ , just let me cum, I need to--”

She obeyed, plunging down as far as she could with her mouth and gripping the rest of his shaft with her other hand. Sans jerked beneath her mouth, letting out a strangled cry when her tongue laved at his cock with fervor.

“Fuck, fuck, I’m gonna-- _you feel so fuckin’ good_ , holy shit!” She made short work of him as he squirmed and pulled taut against the bonds; his fingers twitched, eager to sink themselves into her hair so he could plunge into her mouth recklessly. But she kept a steady pace, all the while looking up at him with something wicked in her eyes, and he looked at her like she was some kind of angel. It wasn’t long until he was gritting his teeth, spine bowed over. “Babe, I’m gonna--I’m…!” With a grunt, his cock pulsed and he came into her mouth, though she only slid down further onto it and took each surge of his magic willingly. It left a tingling feeling down her throat and warmed her chest.

Immediately after, he slumped back on the chair, his grin wide and goofy. She slid her mouth off of him, though his dick didn’t disappear yet. Giving him a wide grin and wiping her lips, she undid the bonds on his hands.

What she didn’t expect was for him to pounce on her right away, snarling and tackling her to their--bed? When had they moved into--

Her thought process hadn’t completed when she suddenly noticed she was on her back, staring wide-eyed up at her boyfriend who had heated intent in his gaze.

“You’re pretty damn good, babe,” he said, wrapping his phalanges around her breast and squeezing roughly. “But I think it’s my turn.” She grinned up him, eyes bright and eager. Her hand pressed to his sternum, where his soul buzzed with energy, and she leaned up to kiss him sweetly.

“I think you’ve earned it,” she said, smiling. His face softened and he cupped her face, thumb stroking near the lipstick-mussed corner of her mouth. She squeaked when he suddenly moved away, hooking his hands under her knees and dragging her to the edge of the bed. He dropped to his knees on the floor between her thighs, nipping at the inside of one of them. She got up on her elbows, watching him with wide eyes, and he chuckled.

“Been waitin’ to do this all day,” he told her, letting his teeth part to expose the glow of his tongue. She whined above him and he tugged her underwear off, pausing only for a moment to get it over the curve of her ass and down her legs. His fingers immediately went to her folds and she took a shaky breath. “God, you loved that, didn’t you? Takin’ charge. Look how fuckin’ wet you are.”

She was trembling now as his mouth got closer to her hot center. He kissed and nipped at one thigh from the knee upwards, his left hand turned palm-up as he slid two fingers inside.

“Sans!” she gasped, gripping the sheet with one hand and mindlessly tweaking her own nipple with the other. She was squirming, trying to get his mouth centered on her, but his firm grip kept her from succeeding.

“Nuh uh, you made me wait, so you do too, ya little tease.” His fingers gave a harsh twist and slid home, eliciting a sharp gasp followed by a long moan from her. “Mmm, tell me what you want, sweetheart.”

She whined above him, twisting the sheets in her hands. “Sans, please…”

“Please what? I can’t give you what you want if I can’t understand you,” he told her, amusement lacing his tone as he threw her earlier words back at her. He also loved getting her to this point; normally, it was hard for her to say anything dirty out loud, but if she was pushed enough…

“God, Sans, I… I need you to…” She bit her lip, flushing in a full-body blush. His thumb brushed against her swollen clit and her back arched at the shock of pleasure it sent up her spine, and suddenly words were tumbling unbidden from her lips. “L-lick me, baby, please, j-just, oh my god _Sans lick my pussy right now or I swear--_ ”

She let out a long, drawn-out groan that sent chills down Sans’s spine as his tongue finally stroked a line from her slit all the way upwards until it settled at her clit. She was panting above him, one hand scrabbling at his skull as if unsure whether to push him away or pull him closer. His arms hooked around her thighs until her ass cheeks practically rested on his shoulders. His tongue made flat, wide strokes across that little bundle of nerves, already so slick with her arousal and only getting wetter. Sans was still hard as a rock beneath her and he was eager to bury himself deep inside her body, but first he was going to give her an earth-shattering orgasm because god _damn_ did he love this woman.

“Ahh, ah…!” Her breathing paused and her body bowed up, tense and squeezing him, and he knew to keep up the pace because-- “ _Sans!_ ” She shuddered as she came, her lover lapping up the flood resulting from it. She whimpered and trembled violently as each wave of her orgasm hit her, until, with a little sigh, her body went limp. He got to his feet, wiping his face on his sleeve and grinning at her eagerly.

Her hair was spread all around her in a mess of tangles, cheeks flushed, chest heaving. The best part, though, was the soft, satisfied expression, full of love just for him. Sans didn’t think he’d ever get used to that. He leaned down to her at the same time as her arms reached up for him, and he kissed her with all the care and adoration he had for her.

“God I love you so much,” he told her, voice hoarse. She stroked his skull, her smile getting wider.

“And I love you, sweetheart.” The skeleton’s eyes softened at her favored pet name for him and he gave her one more sweet kiss.

He stood straight, assuming one of their favorite positions; she automatically scooted down until her butt was almost over the edge, trusting him to catch her legs. He did, swinging them up onto his shoulders and pressing his dick at her soaked entrance. He looked down, waiting for her little nod of consent, before hilting himself deep inside.

He grunted and held that position for a moment, pressing progressively harder and watching her squirm beneath him. For her, his dick was just the right size where it would barely graze her cervix when he pushed all the way in like this; it was the perfect balance between pleasure and pain and it had her seeing stars.

Sans growled quietly, fingers digging into the flesh of her thigh, and pulled out before plunging deep inside again. He watched her mouth drop open as she gave a little cry, fingers curling and uncurling, and he repeated the motion, panting. Her cries only got louder and more insistent with each thrust, and right when her noises began to turn into desperate sobs he moved his hand to thumb at her clit between their bodies.

She gave a guttural, choked scream as she came a second time, her hair sticking to the perspiration on her skin, her lips parted, face flushed, eyes dark. She was the most beautiful thing he’d ever seen like this. Her walls fluttered and pulsed all around him as her orgasm hit her in waves, and his hands dug into her so hard that they would leave bruises for her to find the next day. She was like wet velvet surrounding him, pulling him eagerly deeper inside as if her body wanted all of him as close as possible. He granted its wish as her orgasm tapered off, hilting himself and groaning as he came inside of her.

Her belly warmed with the feeling of his hot magic as he filled her. It was something incredibly intimate and sexy and just for them, and as his knees buckled, he let her legs down and she pulled him down close to her. The two of them stayed like that, just for a few moments, until his cock dissipated and he collapsed into her. She chuckled warmly, letting him fall with his face between her breasts.

She hummed in content, petting his skull as his arms wrapped around and under her body. “Happy anniversary, sweetheart,” she murmured tiredly. He gave her a little squeeze.

“Mmhmm. Happy anniversary, babe. I love you.”

She leaned down, brushing her lips across the top of his skull. “I love you, too. Let’s get cleaned up and head to bed.”

After a quick shower together (full of giggling and playful ass-grabbing from Sans), the two of them dressed into their pajamas and fell into bed facing each other. His fingers stroked her hair and her eyelids drooped lower with each pass. “Goodnight, Sans,” she yawned, closing her eyes and cuddling into his chest. He wrapped his arms around her, feeling more content than he had in years.

“Goodnight, babe. Sweet dreams.”


End file.
